Science and technology in the elastomer field has developed to such an extent that synthetic elastomers have supplemented or replaced natural rubber to a great extent in the fabrication of tires and other rubber products. However, a major deficiency of synthetic elastomers is the lack of sufficient green strength required for satisfactory processing or building properties as in building tires. The abatement of this deficiency has long been sought by the art.
The term “green strength,” while being commonly employed and generally understood by persons skilled in the rubber industry, is nevertheless a difficult property to precisely define. Basically, it is that property of an unvulcanized polymer common in natural rubber which, under normal building conditions where multiple components are employed, results in little or no unwanted distortion of any of the assembled components. Thus, with synthetic polymers or copolymers, adequate green strength, that is the requisite mechanical strength for processing and fabricating operations necessarily carried out prior to vulcanization, is lacking. That is, generally the maximum or “peak” stress which the unvulcanized materials will exhibit during deformation is rather low. Thus, unvulcanized strips or other forms of the elastomer are often distorted during processing or building operations. Although numerous additives and compounds have been utilized in association with various elastomers, substantial improvement in green strength has generally not been accomplished.
Green strength has generally been measured by stress/strain curves of unvulcanized compounds. Usually, the green strength of a compound is indicated by various properties of the stress/strain curve; typically, the average slope beyond the first peak or inflection of the curve, the (ultimate) tensile strength, and the ultimate elongation. Improvements in any one or more of these stress properties indicate improved green strength.